项目另一个列表复制列表 [英] Copy list of items to another list

问题描述

我想要的项目列表，从list1的复制到另一个目录列表2。我能做到这一点。不过，我不希望在列表2砥所作的更改反映在list1的。

I am trying to copy the list of items from list1 to another list list2. I'm able to do that. However I don't want the changes made in list2 tobe reflected in list1.

class Program
{
    static void Main(string[] args)
    {
        List<MyClass> list1 = new List<MyClass>();
        list1.Add(new MyClass(){ID = 1, Name = "name1"});
        list1.Add(new MyClass(){ID = 2, Name = "name2"});
        list1.Add(new MyClass(){ID = 3, Name = "name3"});

        //Copy items from list1 to list2
        List<MyClass> list2 = new List<MyClass>(list1);

        list1.ForEach(x => Console.WriteLine(x.Name));   //It shows the name as added

        //Empty items in list2
        list2.ForEach(x => x.Name = string.Empty);

        //Print items in list1
        list1.ForEach(x => Console.WriteLine(x.Name));   //It shows the name is empty
        Console.ReadKey();
    }
}

class MyClass
{
    private int id;

    public int ID
    {
        get { return id; }
        set { id = value; }
    }

    private string name;

    public string Name
    {
        get { return name; }
        set { name = value; }
    }
}

我希望应该有一个简单的方法。

I hope there should be an easy way.

推荐答案

由于这是您要更改所有引用类型。您需要创建一个复制的该实例：

Since this is a reference type you are changing all. You need to create a copy of that instance:

public class MyClass 
{
    private int id;

    public int ID
    {
        get { return id; }
        set { id = value; }
    }

    private string name;

    public string Name
    {
        get { return name; }
        set { name = value; }
    }

    public MyClass Copy()
    { 
        return new MyClass
        {
            ID = this.ID,
            Name = this.Name
        };
    }
}

现在，你可以以这种方式创建第二个列表：

Now you can create the second list in this way:

List<MyClass> list2 = new List<MyClass>(list1.Select(x => x.Copy()));

当然你不需要这种方法。你可以做到这一点也即时在LINQ查询：

Of course you don't need that method. You could do that also on-the-fly in the LINQ query:

List<MyClass> list2 = new List<MyClass>(list1.Select(x => new MyClass { ID = x.ID, Name = x.Name }));

---

另一个类似的方法是一种的拷贝构造。拷贝构造函数是用来提供相同类型的另一个实例初始化实例：

---

Another similar approach is a copy-constructor. A copy-constructor is used to initialize an instance by providing another instance of the same type:

public class MyClass
{
    private int id;

    public MyClass(MyClass instance)
    {
        this.id = instance.ID;
        this.name = instance.Name;
    }

    public int ID
    {
        get { return id; }
        set { id = value; }
    }

    private string name;

    public string Name
    {
        get { return name; }
        set { name = value; }
    }
}

现在，你可以填写在此份名单方式：

Now you could fill the list with copies in this way:

List<MyClass> list2 = new List<MyClass>(list1.Select(x => new MyClass(x)));

或 List.ConvertAll ：

List<MyClass> list2 = list1.ConvertAll(x => new MyClass(x));

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